codec.rs

use crate::{error::mdbx_result, Error, TransactionKind};
use derive_more::{Deref, DerefMut, Display};
use std::{borrow::Cow, slice};
use thiserror::Error;

/// Implement this to be able to decode data values
pub trait Decodable<'tx> {
    fn decode(data_val: &[u8]) -> Result<Self, Error>
    where
        Self: Sized;

    #[doc(hidden)]
    unsafe fn decode_val<K: TransactionKind>(
        _: *const ffi::MDBX_txn,
        data_val: &ffi::MDBX_val,
    ) -> Result<Self, Error>
    where
        Self: Sized,
    {
        let s = slice::from_raw_parts(data_val.iov_base as *const u8, data_val.iov_len);

        Decodable::decode(s)
    }
}

impl<'tx> Decodable<'tx> for Cow<'tx, [u8]> {
    fn decode(_: &[u8]) -> Result<Self, Error> {
        unreachable!()
    }

    #[doc(hidden)]
    unsafe fn decode_val<K: TransactionKind>(
        txn: *const ffi::MDBX_txn,
        data_val: &ffi::MDBX_val,
    ) -> Result<Self, Error> {
        let is_dirty = (!K::ONLY_CLEAN) && mdbx_result(ffi::mdbx_is_dirty(txn, data_val.iov_base))?;

        let s = slice::from_raw_parts(data_val.iov_base as *const u8, data_val.iov_len);

        Ok(if is_dirty {
            Cow::Owned(s.to_vec())
        } else {
            Cow::Borrowed(s)
        })
    }
}

#[cfg(feature = "lifetimed-bytes")]
impl<'tx> Decodable<'tx> for lifetimed_bytes::Bytes<'tx> {
    fn decode(_: &[u8]) -> Result<Self, Error> {
        unreachable!()
    }

    #[doc(hidden)]
    unsafe fn decode_val<K: TransactionKind>(
        txn: *const ffi::MDBX_txn,
        data_val: &ffi::MDBX_val,
    ) -> Result<Self, Error> {
        Cow::<'tx, [u8]>::decode_val::<K>(txn, data_val).map(From::from)
    }
}

impl Decodable<'_> for Vec<u8> {
    fn decode(data_val: &[u8]) -> Result<Self, Error>
    where
        Self: Sized,
    {
        Ok(data_val.to_vec())
    }
}

impl Decodable<'_> for () {
    fn decode(_: &[u8]) -> Result<Self, Error> {
        Ok(())
    }

    unsafe fn decode_val<K: TransactionKind>(
        _: *const ffi::MDBX_txn,
        _: &ffi::MDBX_val,
    ) -> Result<Self, Error> {
        Ok(())
    }
}

/// If you don't need the data itself, just its length.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, Deref, DerefMut)]
pub struct ObjectLength(pub usize);

impl Decodable<'_> for ObjectLength {
    fn decode(data_val: &[u8]) -> Result<Self, Error>
    where
        Self: Sized,
    {
        Ok(Self(data_val.len()))
    }
}

impl<const LEN: usize> Decodable<'_> for [u8; LEN] {
    fn decode(data_val: &[u8]) -> Result<Self, Error>
    where
        Self: Sized,
    {
        #[derive(Clone, Debug, Display, Error)]
        struct InvalidSize<const LEN: usize> {
            got: usize,
        }

        if data_val.len() != LEN {
            return Err(Error::DecodeError(Box::new(InvalidSize::<LEN> {
                got: data_val.len(),
            })));
        }
        let mut a = [0; LEN];
        a[..].copy_from_slice(data_val);
        Ok(a)
    }
}